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Biodiversity and Evolution
Chapter 4
Core Case Study: Why Should We Care
about the American Alligator?
 Largest reptile in
North America
 1930s: Hunters and
poachers
 Importance of gator holes
and nesting mounds
 1967: endangered species
 1977: comeback, threatened species
Natural Capital: Major Components of
the Earth’s Biodiversity
Where Do Species Come From?
 The scientific theory of evolution explains how
life on earth changes over time through
changes in the genes of populations.
 Populations evolve when genes mutate and
give some individuals genetic traits that
enhance their abilities to survive and to
produce offspring with these traits (NATURAL
SELECTION)
Biological Evolution by Natural Selection
Explains How Life Changes over Time
 Biological evolution
 Natural selection
• Charles Darwin
• Alfred Russel Wallace
 Tree of Life
Evolution by Natural Selection
Three Common Myths about Evolution
through Natural Selection
 “Survival of the fittest” is not “survival of the
strongest”
 Organisms do not develop traits out of need or
want
 No grand plan of nature for perfect adaptation
How Do Geological Processes and
Climate Change Affect Evolution?
 Tectonic plate movements, volcanic eruptions,
earthquakes, and climate change have shifted
wildlife habitats, wiped out large numbers of
species, and created opportunities for the
evolution of new species.
Geologic Processes Affect Natural
Selection
 Tectonic plates affect evolution and the location
of life on earth
• Location of continents and oceans
• Species physically move, or adapt, or form new
species through natural selection
 Earthquakes
 Volcanic eruptions
Movement of the Earth’s Continents
over Millions of Years
Climate Change and Catastrophes Affect
Natural Selection
 Ice ages followed by warming temperatures
 Collisions between the earth and large asteroids
• New species
• Extinction
Changes in Ice Coverage in the Northern
Hemisphere During the last 18,000 Years
How Do Speciation, Extinction, and
Human Activities Affect Biodiversity?
 As environmental conditions change, the
balance between formation of new species and
extinction of existing species determines the
earth’s biodiversity.
 Human activities can decrease biodiversity
by causing the premature extinction of species
and by destroying or degrading habitats
needed for the development of new species.
How Do New Species Evolve?
 Geographic isolation
 Reproductive isolation
Extinction is Forever
 Extinction
 Endemic species
• Particularly vulnerable
Golden Toad of Costa Rica
What Is Species Diversity and Why
Is It Important?
 Species diversity is a major component of
biodiversity and tends to increase the
sustainability of ecosystems.
Species Diversity: Variety, Abundance of
Species in a Particular Place
 Species diversity
• Species richness
• Species evenness
 Diversity varies with geographical location
• Most species-rich communities
•
•
•
•
Tropical rain forests
Coral reefs
Ocean bottom zone
Large tropical lakes
Science Focus: Species Richness
on Islands
 Species equilibrium model - Theory of island
biogeography
• Rate of new species immigrating should balance
with the rate of species extinction
 Island size and distance from the mainland
need to be considered
What Roles Do Species Play in
Ecosystems?
 Each species plays a specific ecological role
called its niche.
 Any given species may play one or more of five
important roles—native, nonnative, indicator,
keystone, or foundation roles—in a particular
ecosystem.
Each Species Plays a Unique Role
in Its Ecosystem
 Ecological niche, niche
• Pattern of living
 Generalist species
• Broad niche
• Ex = Cockroach
 Specialist species
• Narrow niche
• Ex = Panda
Niches Can Be Occupied by Native and
Nonnative Species
 Nonnative species; invasive, alien, or exotic
species
• May spread rapidly
• Not all are villains
• Outcompete native species
• No natural predators
• Underutilized food sources
• Generalists
• Frequent Reproduction
Kudzu
The vine that “ate the
south”
Imported in the 1930’s
from Japan – control soil
erosion – prolific growth –
kills trees
Check out KUD-ZOO!
Indicator Species Serve as Biological
“Smoke Alarms”
 Indicator species
• Can monitor environmental quality
•
•
•
•
Trout
Birds
Butterflies
Frogs
Case Study: Why Are Amphibians
Vanishing?
 Habitat loss and fragmentation
 Prolonged drought
 Pollution
 Increase in UV radiation
 Parasites
 Viral and fungal diseases
 Climate change
 Overhunting
 Nonnative predators and competitors
Case Study: Why Are Amphibians
Vanishing?
 Importance of amphibians
• Sensitive biological indicators of environmental
changes
• Adult amphibians
• Important ecological roles in biological
communities
• Genetic storehouse of pharmaceutical products
waiting to be discovered
Keystone, Foundation Species Determine
Structure, Function of Their Ecosystems
 Keystone species - arch stone, remove & it
collapses
• Pollinators
• Top predator
 Foundation species
• Create or enhance their habitats, which benefit
others
• Elephants
• Beavers
Case Study: Why Should We
Protect Sharks?
 Keystone species
• Eat dead and dying fish in the ocean
• Strong immune systems
• Wounds do not get infected
• Almost never get cancer
• Could help humans if we understood their immune
system